Requestable.swift

protocol Requestable {
    
    associatedtype Element
    
    var httpMethod: HTTPMethod { get }
    var headers: HeadParams? { get }
    var bodyParams: BodyParams? { get }
    
    var encoding: RequestEncoding { get }
    
    var url: String { get }
    
    func getDataFrom(dictionary: NSDictionary) -> Element
    func call(success success: Element -> (), failure: ApiResponse -> ())

    func fillBodyParams()
    func fillHeaders()
}

extension Requestable {
    func call(success success: Element -> (), failure: ApiResponse -> ()) {
        let qos = Int(QOS_CLASS_USER_INTERACTIVE.rawValue)
        
        dispatch_async(dispatch_get_global_queue(qos, 0)) {
            
            var responseHandler = Network.ResponseHandler()
            responseHandler.failureCallback = { apiResponse in
                dispatch_async(dispatch_get_main_queue()) {
                    failure(apiResponse)
                }
            }
            
            responseHandler.successCallback = { dictionary in
                let data = self.getDataFrom(dictionary)
                dispatch_async(dispatch_get_main_queue()) {
                    success(data)
                }
            }
            
            self.fillHeaders()
            self.fillBodyParams()
            
            self.makeTheCall(responseHandler)
        }
    }
    
    private func makeTheCall(responseHandler: Network.ResponseHandler) {
        Network.AlamofireCaller(networkResponseHandler: responseHandler).call(
            url,
            httpMethod: httpMethod,
            encoding: encoding,
            headers: headers,
            bodyParams: bodyParams)
    }
}